REU: Effects of Resource Quality and Microarthropods on Forest Floor Nitrogen Dynamics

资源质量是控制森林生态系统有机质分解和养分释放速率的主要因素。在资源质量和小气候的约束下，分解和营养动态是动物-微生物相互作用的产物。数据表明，微型节肢动物的活动通常会增加叶片凋落物的分解速度，并加强外源氮的固定。该项目的目标是以15N为示踪剂，研究资源质量对分解者群落和森林地表氮通量的影响，并更详细地研究微型节肢动物活动对氮素移动的影响。田间试验将考察资源质量对(1)15N标记的凋落物基质中N的净矿化作用，(2)释放的15N通过森林地面剖面(凋落物N、F层N、土壤活性(微生物)N、土壤慢/被动N和土壤可提取N)的移动的影响；(3)15N标记的外源输入的固定以及随后的矿化和移动；(4)以15N为示踪剂的N从土层到地表凋落物的真菌转移。在即将完成的研究中，从腐烂的基质中排除微节肢动物对分解速度和氮素保留量产生了重大影响。通过在实验室孵化中直接操纵微型节肢动物，并通过测量微型节肢动物-微生物相互作用对以下方面的定量影响，将在更可控的条件下详细研究这种效应的机制：(1)微生物现存量和总异养呼吸，(2)15N标记凋落物中N的矿化作用；(3)15N标记外源输入的固定化。这个研究小组表现出始终如一的卓越和生产力。机构住宿是一流的。这项研究的成果对于更好地管理森林资源以及从根本上了解森林生态系统应具有重要意义。

Resource quality is a major factor controlling rates of organic matter decomposition and nutrient release in forested ecosystems. Within the constraints of resource quality and microclimate, decomposition and nutrient dynamics are the product of faunal-microbial interactions. Activities of microarthropods generally increase decomposition rates of leaf litter and, data suggest, enhance immobilization of exogenous nitrogen. The objectives of this project are to examine the effects of resource quality on the decomposer community and on forest floor N fluxes, using 15N as a tracer, and to examine in more detail the effects of microarthropod activities on nitrogen movement. Field experiments will examine the influence of resource quality on (1) net mineralization of N from 15N-labeled litter substrates, (2) the movement of released 15N through the forest floor profile (litter N, F-layer N, soil active (microbial) N, soil slow/passive N, and soil extractable N); (3) immobilization of 15N-labeled exogenous inputs and subsequent mineralization and movement, and (4) fungal translocation of N from the soil horizon to surface litter using 15N as a tracer. In research now nearing completion, exclusion of microarthropods from decaying substrates has produced a significant effect on decomposition rates and N retention. The mechanisms for this effect will be examined in detail under more controlled conditions, by directly manipulating microarthropods in laboratory incubations, and by measuring the quantitative effects of microarthropod-microbial interactions on: (1) microbial standing stocks and total heterotrophic respiration, (2) mineralization of N from 15N-labeled litter and (3) immobilization of 15N-labeled exogenous inputs. This research group has demonstrated consistent excellence and productivity. Institutional accommodations are first-rate. Products of this research should be of importance to the better management of forest resources as well as to the fundamental understanding of forested ecosystems.